Electrophotographic plate and process using naphthylazo compounds as the primary photoconductor



United States Patent 3,482,970 ELECTROPHOTOGRAPHIC PLATE AND PROCESS USING NAPHTHYLAZO COMPOUNDS AS THE PRIMARY PHOTOCONDUCTOR Warren E. Solodar, Rochester, and Santokh S. Labana,

Webster, N.Y., assignors to Xerox Corporation, Rochester, N.Y., a corporation of New York No Drawing. Filed Jan. 21, 1966, Ser. No. 522,045 Int. Cl. G03g 5/06 US. Cl. 96-1.5 7 Claims ABSTRACT OF THE DISCLOSURE Electrophotographic plates are disclosed comprising certain naphthylazo compounds dispersed in electrically insulating binders. The plates are useful in conventional electrophotographic process.

This invention relates to electrophotography and more pialrticularly to a binder plate useful in electrophotogra- P Y- It is known that images may be formed and developed on the surface of certain photoconductive insulating materials by electrostatic means. The basic electrophotographic process, as taught by Carlson in US. Patent 2,297,691, involves uniformly charging a photoconductive insulating layer and then exposing the layer to a lightand-shadow image which dissipates the charge on the portions of the layer which are exposed to light. The electrostatic latent image formed on the layer corresponds to the configuration of the light-and-shadow image. Alternatively, a latent electrostatic image may be formed on the plate by charging said plate in image configuration. This image is rendered visible by depositing on the imaged layer a finely divided developing material comprising a colorant called a toner and a toner carrier. The powdered developing material will normally be attracted to those portions of the layer which retain a charge, thereby forming a powder image corresponding to the latent electrostatic image. Where the base sheet is relatively inexpensive, such as paper, the powder image may be fixed directly to the plate as by heat or solvent fusing. Alternatively, the powder image may be transferred to a sheet of receiving material, such as paper, and fixed thereon. The above general process is also described in US. Patents 2,357,809; 2,891,011; and 3,079,342.

The photoconductive insulating layer to be effective must be capable of holding an electrostatic charge in the dark and dissipating the charge to a conductive substrate when exposed to light. That various photoconductive insulating materials may be used in making electrophotographic plates is known. Suitable photoconductive insulating materials such as anthracene, sulfur, selenium or mixtures thereof have been disclosed by Carlson in US. Patent 2,297,691. These materials generally have sensitivity in the blue or near ultra-violet range, and all but selenium have a further limitation of being only slightly light-sensitive. For this reason, selenium has been the most commerically accepted material for use in electrophotographic plates. Vitreous selenium, however, while desirable in most aspects, suffers from serious limitations in that its spectral response is somewhat limited to the ultra-violet, blue and green regions of the spectrum and the preparation of vitreous selenium plates requires costly and complex procedures, such as vacuum evaporation. Also, vitreous selenium layers are only meta-stable in that they are readily recrystallized into inoperative crystalline forms at temperatures only slightly in excess of those prevailing in conventional electrophotographic copying machines. Further, selenium plates require the use of a separate conductive substrate layer, preferably with an additional barrier layer deposited thereon before deposition of the selenium photoconductor. Because of these economic and commercial considerations, there have been many recent efforts toward developing photoconductive msulatmg materials other than selenium for use in electrophotographic plates.

It has been proposed that various two-component materials be used in photoconductive insulating layers used in electrophotographic plates. These consist of a photoconductive insulating material in particulate form dispersed in an insulating binder. Where the particles consist of a photoconductive material comprising inorganic crystalline compounds containing a metallic ion, satisfactory photographic speed and spectral response for use in xerographic plates are obtained. However, these plates even when dye-sensitized generally have sensitivities much lower than selenium. These plates are generally considered to be non-reusable since it is necessary to use such high percentages of photoconductive pigment in order to attain adequate sensitivity that it is difiicult to obtain smooth surfaces which lend themselves to efiicient toner transfer and subsequent cleaning prior to reuse. An additional drawback in the use of inorganic pigmentbinder type plates is that they can be charged only by negative and not by positive corona discharge. This property makes them commercially undesirable since negative corona discharge generates much more ozone than positive corona discharge and is generally more difficult to control.

It has been further demonstrated that a wide variety of polycyclic compounds may be used together with suitable resin materials to form photoconductive insulating layers useful in binder-type plates. These plates generally lack sensitivity levels necessary for use in conventional electrophotographic copying devices. In addition, these plates lack abrasion resistance and stability of operation, particularly at elevated temperatures.

In another type plate, inherently photoconductive polymers are used, frequently in combination with sensitizing dyes or Lewis acids, to form photoconductive insulating layers. These polymeric organic photoconductor plates generally have the inherent disadvantages of high cost of manufacture, brittleness, and poor adhesion to supporting substrates. A number of these photoconductive insulating layers have thermal distortion properties which make them undesirable in an automatic electrophotographic apparatus which often includes powerful lamps and thermal fusing devices which tend to heat the electrophotographic plate.

Thus, there is a continuing need for improved photo conductive insulating materials from which stable, sensitive, and reusable electrophotographic plates can be made.

It is, therefore, an object of this invention to provide an electrophotographic plate devoid of the above-noted disadvantages.

Another object of this invention is to provide electrophotographic plates having sensitivities which extend over substantial portions of the visible spectrum.

Still another object of this invention is to provide a reusable electrophotographic plate having a high overall sensitivity and high thermal stability when compared to present commercially available reusable plates.

Yet another object of this invention is to provide a photoconductive insulating material suitable for use in electrophotographic plates in both single use and reusable systems.

Yet another object of this invention is to provide a photoconductive insulating layer for an electrophotographic plate which is substantially resistant to abrasion and has a relatively high distortion temperature.

Yet another further object of this invention is to provide an electrophotographic plate having a wide range of useful physical properties.

The foregoing objects and others are accomplished in accordance with this invention, fundamentally, by providing an electrophotographic plate having a novel photoconductive layer comprising a resin binder and a naphthylazo compound having the general formula:

wherein:

X represents an aromatic or a heterocyclic group, which maybe substituted;

Y and Z each represents H, amido, lower alkoxy, lower alkyl, aryl or heterocylic radicals, which may be substituted; and

the OH group is ortho or para to the azo linkage site.

Compositions having the N=N group are generally known in the art as azo compounds, e.g., azo dyes or pigments. These compounds are generally prepared from amino compounds by the process of diazotization and coupling.

Within the above general formula, certain substituents have been found to give especially desirable results. The preferred sub-class within the above general formula has the formula:

wherein:

R represents an aryl or heterocyclic group, which may be substituted,

R represents hydrogen, an amide, lower alkoxy, lower alkyl or carboxamide radical.

The compounds within this sub-class have been found to, in general, have an especially high degree of electrical photosensitivity and to have especially desirable spectral sensitivity to wave-lengths within the visible range.

The specific compounds within this group showing highest photosensitivity include l-( l-naphthylazo)-2-naphthol; 1-(1'-naphthylazo)-2-hydroxy S-acetamido-naphthalene; 1-hydroxy-2-(p-carboxyphenylazo) 4 isopropoxy-naphthalene and N,N' bis (1-1-naphthylazo-2-hydroxy-8- naphthyl) -adipdiamide.

Any suitable organic binder resin may be used in combination with the compounds of this invention to prepare the photoconductive layer of this invention. In order to be useful the resin used in the present invention should be more resistive than about and preferably more than 10 ohms per centimeter under the condiiions of electro photographic use. Typical resins include: thermoplastics including olefin polymers such as polyethylene and polypropylene; polymers derived from dienes such as polybutyldiene, polyisobutylene, and polychloroprene, vinyl and vinylidene polymers such as polystyrene, styrene-acrilonitrile copolymers, acrilonitrile-butadiene-styrene terpolymers, poly'methylmethacrylate, polyacrylates, polyacrylics, polyacrilonitrile, polyvinylacetate, polyvinyl alcohol, polyvinylchloride, polyvinylcarbazole, polyvinyl ethcrs and polyvinyl ketones; fluorocarbon polymers such as polytetrafluorethylene and polyvinylidene fluoride; heterochain thermoplastics such as polyamides, polyesters, polyurethanes, polypeptides, caesine, polyglycols, polysulfides, and polycarbonates; and cellulosic polymers such as regenerated cellulose, cellulose acetate and cellulose nitrate. Also, thermosetting resins including phenolic resins; amino resins such as ureaformaldehyde resins and melamine-formaldehyde resins; unsaturated polyester resins; epoxy resins, silicone polymers; alkyd resins and furan resins. Various copolymers and mixtures of the abovementioned resins may be used where applicable. In addition to the above-noted resins, any other material may be used if desired.

The naphthylazo compositions may be incorporated into the dissolved or melted binder-resin by any suitable means such as strong shear agitation, preferably with simultaneous grinding. Typical methods include ball milling, roller milling, sand milling, ultra-sonic agitation, high speed blending and any combination of these methods. Any suitable ratio of pigment to resin may be used. On a pigment-dried resin weight basis, the useful range extends from about 1:1 to about 1:20. Best results are obtained at, and therefore, the preferred range is, from about 1:1 to about 1:6.

The use in the present invention of lower pigment to resin ratios represents a highly desirable advantage over the prior art since a smaller amount of the relatively expensive pigment component is required. Also, this permits very smooth adhesive coatings to be obtained because of the high binder content. The small proportion of added material has little effect on the physical properties of the binder-resin. Thus, resins may be chosen having the desired softening range, smoothness, hardness, toughness, solvent resistance, or solubility and the like with assurance that the pigment will not affect these properties to any considerable extent.

When it is desired to coat the pigment-resin film on a substrate, various supporting materials may be used. Suitable materials for this purpose include aluminum, steel, brass, metalized or tin oxide coated glass, semi-conductive plastics and resins, paper and any other convenient material. The plate may be over-coated with any suitable material, if desired. The photoconductive layer may be used in the formation of multi-layer sandwich configurations adjacent a dielectric layer similar to that shown by Golovin, et al., in the publication entitled, A New Photographic Process, Etfected by Means of Combined Electret Layers, Doklady. Akad. Nauk SSSR, vol. 129, No. 5, pages 1008-1011, November-December 1959. The pigment-resin-solvent-slurry (or the pigment-resin-melt) may be applied to conductive substrates by any of the wellknown painting or coating methods, including spraying, flow-coating, knife coating, electro coating, Mayer bar draw-down, dip coating, reverse roll coating, etc. Spraying in an electric field may be preferred for smoothest finish and dip coating may be preferred for convenience in the laboratory. The setting, drying, and/or curing steps for these plates are generally similar to those recommended for films of the particular binders as used for other painting applications. For example, azo pigment-epoxy plates may be cured by adding a cross-linking agent and stoving according to approximately about the same schedule as other baking enamels made with the same resins and similar pigments for paint application.

The thickness of the pigment-binder films may be varied from about 1 to about 100 microns, depending upon the required characteristics. Self-supporting films, for example, cannot be conveniently manufactured in thicknesses thinner than about 10 microns, and are easiest to handle and use in the 15 to micron range. Coatings, on the other hand, are preferably formed in the 5 to 30 micron range. For some compositions and purposes, it is desirable to provide a protective overcoating. This overcoating should usually not exceed the thickness of a photoconductive coating and preferably should be no more than A the thickness of said coating. Any suitable overcoating material may be used, such as bichromated shellac.

The following examples further define and describe the electrophotographic plates of the present invention. Parts and percentages are by weight unless otherwise indicated. The examples below should be considered to illustrate various preferred embodiments of the electrophotographic plates of this invention, of methods of preparing said plates, and of methods of imaging on said plates.

EXAMPLE I A xerographic plate is prepared by initially mixing about 6 parts Luvican M-170, a polyvinyl carbazole resin available from BASF, about 54 parts toluene and about 1 part l-hydroxy-2-(p-carboxyphenylazo)-4 isopropoxy naphthalene. This mixture is put into a glass jar containing a quantity of /s" steel balls and milled on a Red Devil Quickie Mill (Gardner Laboratories) for about /2 hour in order to obtain a homogeneous dispersion. After milling, about 3 parts of cyclohexanone is added to the dispersion and the dispersion is applied onto a sheet of 5 mil aluminum foil (Alcoa ll45-H19) using a No. 36 wire drawdown rod. The coating is then forced air dried at about 100 C. for about 2 hours. The plate is charged to a negative potential of about 240 volts by means of a corona discharge, as described, for example, in U.S. Patent 2,777,957. The charged plate is then contact exposed to a film positive by means of a tungsten lamp having a 3400 K. color temperature. The total exposure is about 50 foot candle seconds. The latent electrostatic image formed on the plate is then developed by cascading pigmented electroscopic marking particles over the plate, by the process described in U.S. Patent 2,618,551. The powder image developed on the plate is electrostatically transferred to a receiving sheet and heat fused thereon by the process described, for example, in U.S. Patent 2,576,047. The image on the receiving sheet is of excellent quality and corresponds to the contact exposed original.

EXAMPLE II A xerographic plate is prepared by initially mixing about 6 parts Lucite 2042, an ethyl methacrylate polymer available from E. I. du Pont de Nemours & 00., about 50 parts of toluene, and about 1 part l-hydroxy-Z-(p-carboxyphenylazo)-4-isopropoxy-naphthalene. This mixture is mixed, coated onto a substrate, and cured as in Example I above. The resulting plate is negatively charged to about 600 volts, then exposed and developed as in Example I above. The total exposure is about 100 foot candle seconds. The resulting image corresponds to the original and is of good quality.

EXAMPLE III A xerographic plate is prepared by initially mixing about 5 parts Aroclor 5460, a blend of chlorinated polyphenyls available from Hercules Chemical Co., about 50 parts toluene, and about 1 part l-hydroxy-Z-(p-carboxyphenylazo)-4-isopropoxynaphthalene. The mixture is mixed, coated onto a substrate, and cured as in Example I above. The plate is charged negatively to a potential of about 140 volts, then is exposed and developed as in Example I above. The exposure here is about 100 foot candle seconds. The resulting image corresponds to the original and is of fair quality, with some background.

EXAMPLE IV A xerographic plate is prepared by initially mixing about 6 parts Luvican M170, about 50 parts toluene and about 1 part l-(1-pyrenylazo)-2-naphthol. The mixture is mixed, coated onto a substrate and cured as in Example I above. The resulting plate is charged negatively to a potential of about 380 volts, exposed and developed as in Example I above. The total exposure here is about 40 foot candle seconds. An image corresponding to the original of good quality results.

EXAMPLE V A xerographic plate is prepared by initially mixing about 2 parts Lucite 2042, about 50 parts toluene, and about 1 part 1-(l'-pyrenylazo)-2-naphthol. This mixture is mixed, coated onto a substrate and cured as in Example I above. The resulting plate is charged to a negative potential of about 400 volts. The charged plate is then exposed and developed as in Example I above. Total exposure here is about 240 foot candle seconds. The resulting image corresponds to the original, is of fair quality but has high background.

EXAMPLE VI A xerographic plate is prepared by initially mixing about 6 parts Luvican M-l70, about 50 parts toluene and about 2 parts 1-(l-naphthylazo)-2-naphthol. This mixture is mixed, coated onto a substrate and cured as in Example I above. The resulting plate is charged to a negative potential of about 400 volts, exposed and developed as in Example I above. The total exposure here is about 100 foot candle seconds. An image of good quality, corresponding to the original results.

EXAMPLE VII A xerographic plate is prepared by initially mixing about 5 parts Aroclor 5460, about 40 parts xylene and about 1 part 1-(1-naphthy1azo)-2-hydroxy-8-acetamidenaphthalene. This mixture is mixed, coated onto a substrate and cured as in Example I above. The resulting plate is charged to a negative potential of about 600 volts. The charged plate is then exposed and developed as in Example I above. Total exposure here is about 100 foot candle seconds. An image of good quality, corresponding to the original results.

EXAMPLE VIII A xerographic plate is prepared by initially mixing about 4 parts Pliolite 8-7, a styrene-butadiene copolymer available from the B. F. Goodrich Company, about 50 parts toluene, and about 1 part N-N-bis-(l l'-naphthylazo-Z-hydroxy-8-naphthol)-adipdiamide. This mixture is mixed, coated onto a substrate, and cured as in Example I above. The resulting plate is charged to a negative potential of about 400 volts. The charged plate is then exposed to an image and developed as in Example I above. An image corresponding to the original, of fair quality but with some background, results.

EXAMPLE IX An epoxy-phenolic binder solution is prepared consisting of about 35 percent Epon 1007, an epoxy resin available from the Shell Chemical Company; about 20 percent Methylon 75201, a phenolic resin available from the General Electric Company; about 5 percent Uformite F240, a urea formaldehyde curing agent, avail able from the Rohm and Haas Company; about 30 percent methylisobutyl ketone, and about 10 percent methyl ethyl ketone. About 55 parts by weight of the above epoxy-phenolic resin blend is mixed with about 60 parts methyl ethyl ketone and about 5 parts l-(p-morpholino phenylazo)-2-hyd0xy-3-naphthani1ide. This mixture is put into a glass jar containing a quantity of /8" steel balls and is milled on a Red Devil Quickie Mill for about 1 hour to obtain a homogeneous dispersion. The dispersion is then applied onto 5 mil aluminum foil (Alcoa 1145- Hl9) using a No. 60 wire wound drawdown bar. The coating is air dried at room temperature for about 5 minutes and forced air dried in an oven for about 2 hours at about C.

The resulting plate is charged to a negative potential of about 400 volts by means of corona discharge. The charged plate is then contact exposed to a film positive by means of an ultra-violet light having a color temperature of 3660 K. The latent electrostatic image formed on the plate is developed by cascade. An image of satisfactory quality, corresponding to the original results.

7 EXAMPLE X About 55 parts of the epoxy-phenolic resin blend described in Example IX is mixed with about 60 parts methyl ethyl ketone and about parts of l-(l-naphtholazo)-2-naphthol, coated onto an aluminum plate and cured as in Example IX.

The plate thus prepared is charged to a negative potential of about 400 volts by corona discharge. The charged plate is contact exposed to a film positive by means of a tungsten light having a 2800 K. color temperature. The resulting electrostatic latent image is developed With electroscopic marking particles, producing an image of excellent quality corresponding to the original.

EXAMPLE XI About 55 parts of the epoxy-phenolic resin blend described in Example IX is mixed with about 60 parts methyl ethyl ketone and about 6 parts l-hydroxy-Z-(psulfonilamido phenylazo)-4-isopropoxy naphthylene. The mixture is dispersed, coated onto an aluminum plate and cured as in Example IX.

The plate thus produced is charged to a negative potential of about 350 volts and contact exposed to a film positive by means of a tungsten lamp having a 2800 K. color temperature. The resulting electrostatic latent image is developed with electroscopic marking particles. The powder image developed on the plate is then electrostatically transferred to a paper sheet and heat fused thereon. The image on the paper sheet is of good quality and corresponds to the contact exposed original.

EXAMPLE XII About 50 parts of the epoxy-phenolic resin blend described in Example IX is mixed with about 60 parts methyl ethyl ketone and about 5 parts l-hydroxy-4-(2'- methyl-4-bariurn sulfonate-5'-chlorophenylazo)naphthylene-Z-carboxylic acid. The solution is mixed, coated onto an aluminum substrate and cured as in Example IX.

The plate thus produced is electrostatically charged to a positive potential of about 300 volts. The charged plate is contact exposed to a positive transparency by means of an ultra-violet lamp having a 3 660 K. color temperature. The electrostatic latent image formed is developed with electrostatic marking particles. An image corresponding to the original of satisfactory quality is produced.

EXAMPLE XIII About 45 parts of the epoxy-phenolic resin blend described in Example IX is mixed with about 60 parts methyl ethyl ketone and about 25 parts N,N-bis-(l-lnaphthylazo 2-hydroxy-8-naphthyl)adipdiamide. The solution is mixed, coated onto an aluminum plate, and cured as in Example IX.

The plate thus prepared is charged to a negative potential of about 400 volts and exposed to a film positive by means of a tungsten lamp having a 2800 K. color temperature. The resulting electrostatic latent image is developed with electroscopic marking particles. An image of good quality, conforming to the original results.

EXAMPLE XIV About 50 parts of the epoxy-phenolic resin blend described in Example IX is mixed with about 60 parts methyl ethyl ketone, about 6 parts N,N'-bis-(1-l'-naphthylazo Z-hydroxy-S-naphthyl)-adipdiamide and about 1 part 2,4,7-trinitro-9-fluorenone. The mixture is milled, coated onto an aluminum substrate and cured as in Example IX.

The plate thus prepared is charged to a negative potential of about 400 volts and exposed to a film positive by means of a tungsten lamp having a 2800" K. color temperature. The resulting electrostatic latent image is developed with electroscopic marking particles. An ex cellent image results, conforming to the original.

Although specific components and proportions have been described in the above examples relating to the use of naphthylazo pigments in xerographic plates, other suitable materials, as listed above, may be used with similar results. In addition, other materials may be added to the naphthylazo pigment compositions or to the pigment-resin compositions to synergize, enhance, or otherwise modify their properties. The pigment compositions and/or the pigment-resin compositions of this invention may be dye-sensitized, if desired, or may be mixed or otherwise combined with other photoconductors, both organic and inorganic.

Other modifications and ramifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure. These are intended to be included within the scope of this invention.

What is claimed is:

1. An electrophotographic plate comprising a conductive substrate coated with an insulating binder having dispersed therein an electrically photosensitive azo compound, said azo compound being present in a pigment to hinder ratio of about 1:1 to 1:20 based on the dry weight of the binder, and having the general formula:

R N=N-R wherein:

the OH group is ortho or para to the azo linkage site;

R is selected from the group consisting of aromatic and heterocyclic radicals; and

R and R are each selected from the group consisting of H, amide, lower alkoxy, lower alkyl, aromatic and heterocyclic radicals.

2. The electrophotographic plate of claim 1 wherein said azo compound has the general formula:

1?; N=NR wherein:

R is selected from the group consisting of aromatic and heterocyclic radicals; and

R is selected from the group consisting of H, amide,

lower alkyl and lower alkoxy radicals.

3. The electrophotographic plate of claim 1 wherein said azo compound is 1-(1'-pyrenylazo)2-naphthol.

4. The electrophotographic plate of claim 1 wherein said azo compound is 1-(l'naphthylazo)2-hydroxy-8- acetamido naphthalene.

5. The electrophotographic plate of claim 1 wherein said azo compound is 1-(1'-naphthylazo)2-naphthol.

6. A process for forming a latent electrostatic charge pattern on an electrophotographic plate comprising a conductive substrate coated with an insulating binder having dispersed therein an electrically photo-sensitive azo compound, said azo compound being present in a pigment to binder ratio of about 1:1 to 1:20 based on the dry weight of the binder, which comprises electrostatically charging said plate and exposing said plate to a pattern of activating electromagnetic radiation; said azo compound having the general formula:

wherein:

the OH group is ortho or para to the azo linkage site,

R is selected from the group consisting of aromatic R is selected from the group consisting of aromatic and heterocyclic radicals; and and heterocyclic radicals; and,

R and R are each selected from the group consisting R and R are each selected from the group consisting of H, amide, lower alkoxy, lower alkyl, aromatic of H, amide, lower alkoxy, lower alkyl, aromatic and heterocyclic radicals. 5 and heterocyclic radicals.

7. The imaging process which comprises forming an electrostatic latent image on an electrophotographic plate References Cited which comprises a conductive substrate coated with an insulating binder having dispersed therein an electrically UNITED STATES PATENTS photosensitive azo compound, said azo compound being 10 4 5 5 5 19 Tulogin et ah 204 1 1 present in a pigment to binder ratio of about 1:1 to 1 :20 2 297 91 10 1942 l 9 1 based on the dry weight of the binder, and developing 244 51 4 1 Neuggbauer et a1.

said latent image with electroscopic marking particles;

said azo compound having the general formula: GEORGE E LESMES Primary Examiner J. C. COOPER III, Assistant Examiner N=N*R US. 01. X.R.

wherein:

the OH group is ortho or para to the azo linkage site; 

